Personal watercrafts are a popular type of watercraft in which one or more passengers ride on, rather than in, the watercraft.
Frequently, these watercrafts are sporting in nature, and the riders expect to leave the watercraft at times during its use and enter into the body of water in which the watercraft is operating.
A relatively small hull of a personal watercraft defines a rider's area above an engine compartment. An internal combustion engine powers a jet propulsion unit, which propels the watercraft. The engine lies within the engine compartment in front of a tunnel formed on an underside of the hull. The jet propulsion unit, which includes an impeller, is placed within the tunnel. The impeller has an impeller shaft driven by the engine. The impeller shaft usually extends between the engine and the jet propulsion device through a bulkhead of the hull tunnel.
Personal watercraft with four-cycle engines are now being produced primarily for reducing exhaust emissions. The four-cycle engine desirably includes a plenum chamber that has a relatively large volume so as to obtain high performance under all running conditions. The four-cycle engine, however, has two or more valves and a valve drive mechanism, as well as the forgoing throttle bodies, which are factors that make the engine larger in height and/or width. On the other hand, because the rider's seat is defined above the engine compartment as noted above, the capacity and height of the engine compartment is limited. Otherwise, the seat position must be higher and/or wider which may not be comfortable for the rider.
In order for a personal watercraft to operate, the engine requires sufficient ventilation, i.e. circulation of air. Existing watercraft have employed various ventilation arrangements, however, none of these efficiently utilize the limited space within the hull or take account of the need for ease of assembly of the watercraft. In addition, intrusion of water into the hull in a roll-over condition is of concern.
Accordingly, it is important to make efficient use of the available space within the engine compartment defined by the hull of the watercraft so as to accommodate the necessary engine components within a hull sized to provide a comfortable seating position to the rider and any passengers. In addition, the overall center of gravity of the watercraft must be considered in the engine arrangement so as to not negatively affect the watercraft's handling. Furthermore, with limited access to the engine compartment, the engine and component arrangement preferably accommodates access to components of the engine which require routine maintenance. In addition, it is desirable to provide an air ventilation system that limits the intrusion of water into the hull of the craft in a roll-over condition.
In addition to supplying air to the engine for its combustion and discharge of the exhaust gases from the engine, it is further desirable to provide additional air ventilation for the engine compartment. That is, it is desirable to provide a continuous form of air circulation through the engine compartment in addition to the air that is consumed by the engine for its combustion. Such ventilation of the engine compartment assists in removing unwanted vapors from the engine compartment and also helps insure an adequate engine cooling and cooling of the other components in the engine compartment which do not have their own cooing systems.